In a batch processing chamber, film thickness, refractive index and wet etch rate uniformity are mostly dependent on pocket temperature variations in the radial and azimuthal directions. Some deposited films, like SiN, are very sensitive to thermal gradients and uniformity inside the pocket in both directions. Thermal non-uniformity is more predominant than RF non-uniformity on most films. Some current batch process chambers using carousel susceptors with one slit valve, five zone heater coils are not enough to compensate for large thermal gradients (>10° C.) on the wafer even with zonal tuning and susceptor rotation. This may be due, in part, to cold spots near the slit valve and lift pins.
Current SiC coated graphite susceptors are large, monolithic and expensive to clean. In order to get the susceptor cleaned, a spare susceptor is kept to minimize chamber downtime. Whenever a new susceptor is installed, the flatness, runout and other measurements are documents. SiC coated materials are resistance to aqueous solutions of salts, organic reagents, some dilute acids (e.g., dilute HF, HCl, H2SO4, HNO3) and hot inert gases. However, the SiC coating by itself is not inert and erodes faster under NF3 plasma or fluorine, HF environments.
Therefore, there is a need in the art for apparatus and methods to increase temperature uniformity across the wafer. There is also a need in the art for susceptors inert to the chamber environment.